Such an actuator serves to vary the position of an aerodynamic surface (or member) such as a helicopter rotor blade or an aircraft aileron as a function of a position setpoint signal for said surface, which signal may be delivered by an on-board flight control computer.
The invention applies in particular to an electrical servo-control comprising a rotary electric motor driving a mechanical member in translation via a screw/nut type speed-reducing gear.
The invention applies in particular to an actuator connected mechanically in series with, i.e. interposed between, a flight control member suitable for being actuated by a pilot and the aerodynamic surface of position that is to be adjusted.
The use of such a so-called “series” actuator is described in particular in patent U.S. Pat. No. 4,492,907 where a position servo-control circuit for the actuator includes a circuit for monitoring the position of the member driven by the servo-motor, which position can be measured in particular by means of a potentiometer.
Besides, patent U.S. Pat. No. 5,204,605 describes such an actuator in which the position of the actuator is calculated as a function of signals delivered by Hall effect sensors that are sensitive to the position of the rotor of the actuator's motor, and in which the position corresponding to the mid-point (i.e. half-stroke) of the actuator is detected by another Hall effect sensor.
Since the reliability of systems on board an aircraft is crucial, proposals are also made in patent U.S. Pat. No. 4,434,389 for an aircraft control surface servo-motor in which the stator of the motor includes redundant coils and independent sets of position sensors (Hall effect sensors).